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rfc:rfc3087

Network Working Group B. Campbell Request for Comments: 3087 R. Sparks Category: Informational dynamicsoft

                                                            April 2001
          Control of Service Context using SIP Request-URI

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 This memo provides information for the Internet community.  It
 describes a useful way to conceptualize the use of the standard SIP
 (Session Initiation Protocol) Request-URI (Uniform Resource
 Identifier) that the authors and many members of the SIP community
 think is suitable as a convention.  It does not define any new
 protocol with respect to RFC 2543.
 In a conventional telephony environment, extended service
 applications often use call state information, such as calling party,
 called party, reason for forward, etc, to infer application context.
 In a SIP/2.0 call, much of this information may be either non-
 existent or unreliable.  This document proposes a mechanism to
 communicate context information to an application.  Under this
 proposal, a client or proxy can communicate context through the use
 of a distinctive Request-URI.  This document continues with examples
 of how this mechanism could be used in a voice mail application.

Campbell & Sparks Informational [Page 1] RFC 3087 SIP Service Control April 2001

Table of Contents

 1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  3
 2.      Example Application  . . . . . . . . . . . . . . . . . . .  3
 2.1     Using URIs to Control Voice Mail Service Behavior  . . . .  3
 3.      Voice Mail Scenario Descriptions . . . . . . . . . . . . .  5
 3.1     Deposits . . . . . . . . . . . . . . . . . . . . . . . . .  5
 3.1.1   Direct Request to Deposit to a particular mailbox  . . . .  5
 3.1.1.1 SIP source . . . . . . . . . . . . . . . . . . . . . . . .  5
 3.1.1.2 Arbitrary PSTN source  . . . . . . . . . . . . . . . . . .  5
 3.1.1.3 Recognized PSTN source . . . . . . . . . . . . . . . . . .  6
 3.1.2   Direct Request to Deposit, mailbox to be determined  . . .  6
 3.1.2.1 SIP source . . . . . . . . . . . . . . . . . . . . . . . .  6
 3.1.2.2 PSTN source  . . . . . . . . . . . . . . . . . . . . . . .  6
 3.1.2.3 Indirect Request to Deposit, due to find-me proxy decision  6
 3.2     Retrievals . . . . . . . . . . . . . . . . . . . . . . . .  7
 3.2.1   Request to Retrieve from a particular mailbox  . . . . . .  7
 3.2.1.1 Trusted SIP source . . . . . . . . . . . . . . . . . . . .  7
 3.2.1.2 Authenticated SIP source . . . . . . . . . . . . . . . . .  7
 3.2.1.3 Unauthenticated SIP source . . . . . . . . . . . . . . . .  7
 3.2.1.4 PSTN source  . . . . . . . . . . . . . . . . . . . . . . .  7
 3.2.2   Request to Retrieve, mailbox to be determined  . . . . . .  7
 3.2.2.1 SIP source . . . . . . . . . . . . . . . . . . . . . . . .  7
 3.2.2.2 Arbitrary PSTN source  . . . . . . . . . . . . . . . . . .  8
 3.2.2.3 Recognized PSTN source . . . . . . . . . . . . . . . . . .  8
 4.      Voice Mail Call Flow Examples  . . . . . . . . . . . . . .  8
 4.1     Generic Scenario . . . . . . . . . . . . . . . . . . . . .  8
 4.1.1   Direct call to the voice mail system . . . . . . . . . . .  8
 4.2     Message Deposit Scenarios  . . . . . . . . . . . . . . . . 13
 4.2.1   Call to known subscriber forwarded on no answer  . . . . . 13
 4.2.2   Call to known subscriber forwarded on busy . . . . . . . . 19
 4.2.3   Direct call to a subscriber's mailbox  . . . . . . . . . . 24
 4.3     Message Retrieval Scenarios  . . . . . . . . . . . . . . . 29
 4.3.1   Call to retrieve messages believed to be from a known
         subscriber . . . . . . . . . . . . . . . . . . . . . . . . 29
 4.3.2   Call to retrieve messages from an authenticated subscriber 33
 5.      Security Considerations  . . . . . . . . . . . . . . . . . 38
 6.      Acknowledgments  . . . . . . . . . . . . . . . . . . . . . 38
         References . . . . . . . . . . . . . . . . . . . . . . . . 38
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . 38
         Full Copyright Statement . . . . . . . . . . . . . . . . . 39

Campbell & Sparks Informational [Page 2] RFC 3087 SIP Service Control April 2001

1. Introduction

 A communication service should make use of the information it has at
 hand when being accessed.  For example, in most current voice mail
 implementations, a subscriber retrieving messages from his own desk
 does not have to reenter his voice mailbox number - the service
 assumes that the store being accessed is the one associated with the
 endpoint being used to access the service.  Some services allow the
 user to validate this assumption using IVR techniques before
 prompting for a PIN.
 This concept of context-awareness can be captured in a voice mail
 service implementing SIP as defined in RFC 2543[1], without
 modification, through the standard use of that protocol's Request-
 URI.  Furthermore, the concept is applicable to any SIP-based service
 where initial application state should be determined from context.
 This concept is a usage convention of standard SIP as defined in RFC
 2543[1] and does not modify or extend that protocol in any way.

2. Example Application

 In this document, we use the example of voice mail to illustrate the
 technique.  One motivation for applying this technique to this
 problem is allowing a proxy or location server to control the initial
 state of a voice service.  For example, a voice client might register
 a contact list ending with the URL that would accept voice messages
 for the client.

2.1 Using URIs to Control Voice Mail Service Behavior

 Many conventional voice mail systems use call state information, such
 as the calling party, called party, reason for forward, etc, to
 decide the initial application state.  For example, it might play one
 outgoing message if the call reached voice mail because the called
 party did not answer and another if the line was busy.  It decides
 whom the message is for based on the called party information.  If
 the call originated from a subscriber's phone number, it might
 authenticate the caller and then go directly to the message retrieval
 and account maintenance menu.
 When a new subscriber is added to a system, a set of identities could
 be generated, each given a unique sip URI.  The following tables show
 some of the identities that might be generated (it is not
 exhaustive).  The example schemes show that the URIs could, but don't
 necessarily have to, have mnemonic value.

Campbell & Sparks Informational [Page 3] RFC 3087 SIP Service Control April 2001

 In practical applications, it is important that an application does
 not apply semantic rules to the various URIs.  Instead, it should
 allow any arbitrary string to be provisioned, and map the string to
 the desired behavior.  The owner of the system may choose to
 provision mnemonic strings, but the application should not require
 it.  In any large installation, the system owner is likely to have
 pre-existing rules for mnemonic URIs, and any attempt by an
 application to define its own rules may create a conflict.  For our
 example, this means a voice mail system should allow an arbitrary mix
 of URLs from these schemes, or any other scheme that renders valid
 SIP URIs to be provisioned, rather than enforce one particular
 scheme.
    URI Identity       Example Scheme 1
                            Example Scheme 2
                                 Example Scheme 3
    Deposit with       sip:sub-rjs-deposit@vm.wcom.com
    standard greeting       sip:677283@vm.wcom.com
                                 sip:rjs@vm.wcom.com;mode=deposit
    Deposit with on    sip:sub-rjs-deposit-busy.vm.wcom.com
    phone greeting          sip:677372@vm.wcom.com
                                 sip:rjs@vm.wcom.com;mode=3991243
    Deposit with       sip:sub-rjs-deposit-sg@vm.wcom.com
    special greeting        sip:677384@vm.wcom.com
                                 sip:rjs@vm.wcom.com;mode=sg
    Retrieve - SIP     sip:sub-rjs-retrieve@vm.wcom.com
    authentication          sip:677405@vm.wcom.com
                                 sip:rjs@vm.wcom.com;mode=retrieve
    Retrieve - prompt  sip:sub-rjs-retrieve-inpin.vm.wcom.com
    for PIN in-band         sip:677415@vm.wcom.com
                                 sip:rjs@vm.wcom.com;mode=inpin
 When a service is first set up, identities such as the following
 could be created.
    URI Identity       Example Scheme 1
                            Example Scheme 2
                                 Example Scheme 3
    Deposit -          sip:deposit@vm.wcom.com
    identify target         sip:670001@vm.wcom.com
    mailbox by To:               sip:deposit@vm.wcom.com

Campbell & Sparks Informational [Page 4] RFC 3087 SIP Service Control April 2001

    Retrieve -         sip:retrieve@vm.wcom.com
    identify target         sip:670002@vm.wcom.com
    mailbox by SIP               sip:retrieve@vm.wcom.com
    authentication
    Deposit - prompt   sip:deposit-in@vm.wcom.com
    for target              sip:670003@vm.wcom.com
    mailbox in-band              sip:deposit@vm.wcom.com;mode=inband
    Retrieve - prompt  sip:retrieve-in@vm.wcom.com
    for target              sip:670004@vm.wcom.com
    mailbox and PIN              sip:retrieve@vm.wcom.com;mode=inband
    in-band
 In addition to providing this set of URIs to the subscriber (to use
 as he sees fit), an integrated service provider could add these to
 the set of contacts in a find-me proxy.  The proxy could then route
 calls to the appropriate URI based on the origin of the request, the
 subscriber's preferences and current state.

3. Voice Mail Scenario Descriptions

 In each of these scenarios, the PSTN gateway is configured to
 communicate only with a particular proxy-registrar.

3.1 Deposits

3.1.1 Direct Request to Deposit to a particular mailbox

3.1.1.1 SIP source

 A SIP client that knew the URI for a particular deposit mailbox
 (sip:sub-rjs-deposit@vm.wcom.com) could place a direct invitation to
 the voicemail service, or through a protecting proxy.  The proxy
 could restrict access to deposit identities with special greetings by
 authenticating the requester.

3.1.1.2 Arbitrary PSTN source

 The gateway's proxy would map a call from an unrecognized PSTN number
 to a number associated with a subscriber's mailbox into an invite to
 the deposit with standard greeting URI (sip:sub-rjs-
 deposit@vm.wcom.com).

Campbell & Sparks Informational [Page 5] RFC 3087 SIP Service Control April 2001

3.1.1.3 Recognized PSTN source

 The gateway's proxy would map a call from a recognized (exact or
 pattern match) PSTN number to a number associated with a subscriber's
 mailbox into an invite to the appropriate special greeting URI
 (sip:sub-rjs-deposit-sg@vm.wcom.com).  The gateway's ability to
 identify the calling party (using calling party number) is trusted,
 so no further authentication of the requester is performed.

3.1.2 Direct Request to Deposit, mailbox to be determined

3.1.2.1 SIP source

 A voice mail service or its protecting proxy could expose a generic
 deposit URL for use when a caller wished to go directly to voice
 mail.  The service would likely play an IVR dialog to determine what
 message store to deposit a message into.
 An application designer may be tempted to attempt to match the To:
 and From: headers on a call to infer information.  However, this
 approach could cause complications when multiple proxy forwards occur
 in a call.  For example, A calls B, who has all calls forwarded to C.
 C forwards the call to her voice mail service.  If the voice mail
 service matches the To: header to determine the message store, it
 will get the information for B instead of C.  But there is no reason
 to assume that C's voice mail service has any knowledge of B.

3.1.2.2 PSTN source

 The gateway's proxy would map a call from an unrecognized PSTN number
 to the top level voice mail service access number to an invite to the
 Deposit - prompt for target mailbox in-band URI (sip:deposit-
 in@vm.wcom.com for example).  Getting the call to the target mailbox
 would proceed as in the SIP source case.

3.1.2.3 Indirect Request to Deposit, due to find-me proxy decision

 A find-me proxy could map an invitation to a subscriber
 (sip:rjs@wcom.com) to the appropriate voice mail service URI
 depending on the subscriber's current state.  The normal deposit URI
 could be chosen if the subscriber's contact list has been otherwise
 exhausted with no answer.  The busy-announcement URI would be chosen
 when a busy everywhere response is received from one of the contacts.
 A DND announcement URI could be selected if the subscriber had
 activated DND. Calls to sip:receptionist@wcom.com could be configured
 to roll to sip:deposit@wcom.com

Campbell & Sparks Informational [Page 6] RFC 3087 SIP Service Control April 2001

3.2 Retrievals

3.2.1 Request to Retrieve from a particular mailbox

3.2.1.1 Trusted SIP source

 A request to retrieve the contents of a particular mailbox (sip:sub-
 rjs-retrieve@vm.wcom.com) coming from a trusted source could be
 honored without further authentication checks.  A trusted source is
 one with which the voice mail service has secure communications, and
 to which it is willing to delegate authentication.  This could be the
 service's protecting proxy for example.

3.2.1.2 Authenticated SIP source

 A service, or its protecting proxy, could choose to honor a retrieve
 request for a particular mailbox (sip:sub-rjs-retrieve@vm.wcom.com)
 based on SIP authentication.  If SIP level authentication failed, the
 service or proxy could be configured to send the call to the in-band
 pin prompting URI (sip:sub-rjs-retrieve-inpin@vm.wcom.com).

3.2.1.3 Unauthenticated SIP source

 A service, or its protecting proxy, receiving a retrieve request for
 a particular mailbox (sip:sub-rjs-retrieve@vm.wcom.com) with no other
 method of authenticating the requestor could send the request to the
 in-band pin prompting URI (sip:sub-rjs-retrieve-inpin@vm.wcom.com).

3.2.1.4 PSTN source

 This scenario assumes that the service provider's network has been
 configured such that a PSTN number could be dialed explicitly for
 retrieving messages from a particular mailbox.  Such services
 currently exist, but are not common.  In such a network, the
 gateway's proxy would map the call to the in-band pin prompting URI
 (sip:sub-rjs-retrieve-inpin@vm.wcom.com).

3.2.2 Request to Retrieve, mailbox to be determined

3.2.2.1 SIP source

 As in the Request to Deposit scenario, when a service receives a
 request for the top level retrieve URI it would most likely need to
 use in-band IVR techniques to determine the target mailbox and
 authenticate the caller.

Campbell & Sparks Informational [Page 7] RFC 3087 SIP Service Control April 2001

3.2.2.2 Arbitrary PSTN source

 This scenario assumes there is a single PSTN number that subscribers
 dial to access the voice mail service to retrieve messages.  This is
 the most common access method provided by current voice mail
 services.
 The gateway's proxy would map a call to the top level PSTN number to
 the top level retrieve in-band prompting URI (sip:retrieve-
 in@vm.wcom.com).  Once the system identifies the target mailbox, the
 call would be transferred to the appropriate in-band pin prompting
 URI (sip:sub-rjs-retrieve-inpin@vm.wcom.com).

3.2.2.3 Recognized PSTN source

 This scenario also assumes there is a single PSTN number that
 subscribers dial to access the voice mail service to retrieve
 messages.
 The gateway's proxy would recognize the calling party number as a
 subscriber, and map the call to the subscriber's in-band prompting
 URI (sip:sub-rjs-retrieve-inpin@vm.wcom.com)

4. Voice Mail Call Flow Examples

 The following section describes some example call flows for a
 hypothetical voice mail service, with the host name of vm.wcom.com.
 All the call flows assume that a proxy protects the voice mail
 service and that a trust relationship exists between the voice mail
 service and the proxy.

4.1 Generic Scenario

4.1.1 Direct call to the voice mail system

 User A calls the voice mail system directly.  The voice mail system
 invokes the top-level menu, which might prompt the caller for an
 extension or the first few letters of a name.

Campbell & Sparks Informational [Page 8] RFC 3087 SIP Service Control April 2001

          User A              Proxy               VM Service
            |                   |                       |
            |  INVITE F1        |                       |
            |------------------>|                       |
            |                   |  INVITE F2            |
            | (100 Trying) F3   |---------------------->|
            |<------------------|                       |
            |                   |  180 Ringing F4       |
            |  180 Ringing F5   |<----------------------|
            |<------------------|                       |
            |                   |  200 OK F6            |
            |  200 OK F6        |<----------------------|
            |<------------------|                       |
            |                   |                       |
            |  ACK F8           |                       |
            |------------------>|  ACK F9               |
            |                   |---------------------->|
            |                   |                       |
            |      RTP Established- Play top level menu |
            |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
            |                   |                       |
            |  BYE F10          |                       |
            |------------------>|  BYE F11              |
            |                   |---------------------->|
            |                   |                       |
            |                   |  200 OK F12           |
            |                   |<----------------------|
            |  200 OK F13       |                       |
            |<------------------|                       |
            |                   |                       |
   Flow Id                            Comments
  INVITE F1     INVITE sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Proxy-Authorization:Digest username="UserA",
                realm="MCI WorldCom SIP",
                nonce="ea9c8e88df84f1cc4e341ae6cbe5a359", opaque="",
                uri="sip:VoiceMail@wcom.com", response=<appropriately
                calculated hash goes here>
                Content-Type: application/sdp
                Content-Length: <appropriate value>

Campbell & Sparks Informational [Page 9] RFC 3087 SIP Service Control April 2001

                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
                /*Client for A prepares to receive data on port 49170
                from the network. */
  INVITE F2     INVITE sip:top@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  (100 Trying   SIP/2.0 100 Trying
  F3            Via: SIP/2.0/UDP here.com:5060
  Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  180 Ringing   SIP/2.0 180 Ringing
  F4            Via: SIP/2.0/UDP wcom.com:5060; branch=1
  VM->Proxy     Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0

Campbell & Sparks Informational [Page 10] RFC 3087 SIP Service Control April 2001

  180 Ringing   SIP/2.0 180 Ringing
  F5            Via: SIP/2.0/UDP here.com:5060
  Proxy->A      From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  200 OK F6     SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: VoiceMailSystem <sip:top@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F7     SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact VoiceMailSystem <sip:top@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000

Campbell & Sparks Informational [Page 11] RFC 3087 SIP Service Control April 2001

  ACK F8        ACK sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip:top@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
  ACK F9        ACK sip:top@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>; tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
                /* RTP streams are established between A and VM.  VM
                system starts IVR dialog for top level menu */
                /* User A Hangs Up with VM system.  Alternatively, the
                VM system could initiate the BYE*/
  BYE F10       BYE sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip: top@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  BYE F11       BYE sip: top@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F12    SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com

Campbell & Sparks Informational [Page 12] RFC 3087 SIP Service Control April 2001

                CSeq: 2 BYE
                Content-Length: 0
  200 OK F13    SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq:  2 BYE
                Content-Length: 0

4.2 Message Deposit Scenarios

4.2.1 Call to known subscriber forwarded on no answer

 User A attempts to call UserB, who does not answer.  The call is
 forwarded to UserB's mailbox, and the voice mail system plays UserB's
 outgoing message for a ring-no-answer.  The flow assumes that the URL
 of "sip:UserB-dep-fna@vm.wcom.com maps" to the desired behavior for
 depositing a message on a forward-no-answer.

Campbell & Sparks Informational [Page 13] RFC 3087 SIP Service Control April 2001

    User A            Proxy              User B         VM System
      |                 |                  |                |
      |  INVITE F1      |                  |                |
      |---------------->|  INVITE F2       |                |
      |                 |----------------->|                |
      | (100 Trying) F3 |                  |                |
      |<----------------| 180 Ringing F4   |                |
      |                 |<-----------------|                |
      |  180 Ringing F5 |                  |                |
      |<----------------| (Request Timeout)|                |
      |                 |                  |                |
      |                 | Cancel F6        |                |
      |                 |----------------->|                |
      |                 |                  |                |
      |                 | 200 OK F7        |                |
      |                 |<-----------------|                |
      |                 |                  |                |
      |                 |         INVITE F8                 |
      |                 |---------------------------------->|
      |                 |                  |                |
      |                 |         200 OK F9|                |
      |  200 OK F10     |<----------------------------------|
      |<----------------|                  |                |
      |                 |                  |                |
      |  ACK F11        |                  |                |
      |---------------->|         ACK F12  |                |
      |                 |---------------------------------->|
      |                 |                  |                |
      |    RTP Established Both Ways-Deposit Msg for B      |
      |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
      |                 |                  |                |
      |  BYE F13        |                  |                |
      |---------------->|         BYE F14  |                |
      |                 |---------------------------------->|
      |                 |                  |                |
      |                 |         OK F15   |                |
      |  OK F16         |<----------------------------------|
      |<----------------|                  |                |
      |                 |                  |                |
   Flow Id                            Comments
  INVITE F1     INVITE sip:UserB@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com

Campbell & Sparks Informational [Page 14] RFC 3087 SIP Service Control April 2001

                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Proxy-Authorization:Digest username="UserA",
                realm="MCI WorldCom SIP",
                nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                uri="sip:UserB@wcom.com", response=<appropriately
                calculated hash goes here>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
                /*Client for A prepares to receive data on port 49170
                from the network. */
  INVITE F2     INVITE sip:UserB1@somewhere.wcom.com SIP/2.0
  Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  (100 Trying   SIP/2.0 100 Trying
  F3            Via: SIP/2.0/UDP here.com:5060
  Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0

Campbell & Sparks Informational [Page 15] RFC 3087 SIP Service Control April 2001

  180 Ringing   SIP/2.0 180 Ringing
  F4            Via: SIP/2.0/UDP wcom.com:5060; branch=1
  B1->Proxy     Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  180 Ringing   SIP/2.0 180 Ringing
  F5            Via: SIP/2.0/UDP here.com:5060
  Proxy->A      From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
                /* B1 rings for 9 seconds, this duration is a
                configurable parameter in the Proxy Server.  Proxy
                sends Cancel and proceeds down the list of routes,
                eventually hitting the voice mail URI for forward no
                answer */
  CANCEL F6     CANCEL sip:UserB1@wcom.com SIP/2.0
  Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 CANCEL
                Content-Length: 0
  200 OK F7     SIP/2.0 200 OK
  B1->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 CANCEL
                Content-Length: 0
  INVITE F8     INVITE sip:UserB-dep-fna@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060;branch=2
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE

Campbell & Sparks Informational [Page 16] RFC 3087 SIP Service Control April 2001

                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F9     SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=2
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheLittleGuyVoiceMail <sip:UserB-dep-
                fna@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F10    SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheLittleGuyVoiceMail <sip:UserB-dep-
                fna@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com

Campbell & Sparks Informational [Page 17] RFC 3087 SIP Service Control April 2001

                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  ACK F11       ACK sip:UserB@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip: UserB-dep-fna@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
  ACK F12       ACK sip:UserB-dep-fna@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
                /* RTP streams are established between A and B2.  VM
                system starts IVR dialog for message-deposit on no-
                answer for UserB */
                /* User A Hangs Up with VM system.  Alternatively, the
                VM system could initiate the BYE*/
  BYE F13       BYE sip:UserB@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip: UserB-dep-fna@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  BYE F14       BYE sip: UserB-dep-fna@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0

Campbell & Sparks Informational [Page 18] RFC 3087 SIP Service Control April 2001

  200 OK F15    SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F16    SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq:  2 BYE
                Content-Length: 0

4.2.2 Call to known subscriber forwarded on busy

 User A attempts to call UserB, who is busy.  The call is forwarded to
 UserB's mailbox, and the voice mail system plays UserB's outgoing
 message for a busy.  This flow assumes that "sip:UserB-dep-
 fb@vm.wcom.com" maps to UserB's mailbox and the behavior of "deposit
 message on busy."

Campbell & Sparks Informational [Page 19] RFC 3087 SIP Service Control April 2001

    User A            Proxy              User B         VM System
      |                 |                  |                |
      |  INVITE F1      |                  |                |
      |---------------->|  INVITE F2       |                |
      |                 |----------------->|                |
      | (100 Trying) F3 |                  |                |
      |<----------------| 486 Busy Here F4 |                |
      |                 |<-----------------|                |
      |                 |                  |                |
      |                 |  ACK F5          |                |
      |                 |----------------->|                |
      |                 |                  |                |
      |                 |         INVITE F6                 |
      |                 |---------------------------------->|
      |                 |                  |                |
      |                 |         200 OK F7|                |
      |  200 OK F8      |<----------------------------------|
      |<----------------|                  |                |
      |                 |                  |                |
      |  ACK F9         |                  |                |
      |---------------->|         ACK F10  |                |
      |                 |---------------------------------->|
      |                 |                  |                |
      |    RTP Established Both Ways-Deposit Msg for B      |
      |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
      |                 |                  |                |
      |  BYE F11        |                  |                |
      |---------------->|         BYE F12  |                |
      |                 |---------------------------------->|
      |                 |                  |                |
      |                 |         OK F13   |                |
      |  OK F14         |<----------------------------------|
      |<----------------|                  |                |
      |                 |                  |                |
   Flow Id                            Comments
  INVITE F1     INVITE sip:UserB@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Proxy-Authorization:Digest username="UserA",
                realm="MCI WorldCom SIP",
                nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                uri="sip:UserB@wcom.com", response=<appropriately

Campbell & Sparks Informational [Page 20] RFC 3087 SIP Service Control April 2001

                calculated hash goes here>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
                /*Client for A prepares to receive data on port 49170
                from the network. */
  INVITE F2     INVITE sip:UserB1@somewhere.wcom.com SIP/2.0
  Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  (100 Trying   SIP/2.0 100 Trying
  F3            Via: SIP/2.0/UDP here.com:5060
  Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  486 Busy      SIP/2.0 486 Busy Here
  Here F4       Via: SIP/2.0/UDP wcom.com:5060;branch=1
  B1->Proxy     Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456

Campbell & Sparks Informational [Page 21] RFC 3087 SIP Service Control April 2001

                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  ACK F5        ACK sip: UserB1@wcom.com SIP/2.0
  Proxy->B      Via: SIP/2.0/UDP wcom.com:5060; branch=1
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
  INVITE F6     INVITE sip:UserB-dep-fb@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060;branch=2
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F7     SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=2
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheLittleGuyVoiceMail <sip:UserB-dep-
                fb@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP

Campbell & Sparks Informational [Page 22] RFC 3087 SIP Service Control April 2001

                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F8     SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact TheLittleGuyVoiceMail <sip:UserB-dep-
                fb@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  ACK F9        ACK sip:UserB@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip:UserB-dep-fb@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
  ACK F10       ACK sip:UserB-dep-fb@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
                /* RTP streams are established between A and B2.  VM
                system starts IVR dialog for message-deposit on busy
                for UserB */

Campbell & Sparks Informational [Page 23] RFC 3087 SIP Service Control April 2001

                /* User A Hangs Up with VM system.  Alternatively, the
                VM system could initiate the BYE*/
  BYE F11       BYE sip:UserB@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route: <sip:UserB-dep-fnb@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  BYE F12       BYE sip: UserB-dep-fnb@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F13    SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F14    SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq:  2 BYE
                Content-Length: 0

4.2.3 Direct call to a subscriber's mailbox

 User A calls UserB's mailbox directly.  This flow assumes that
 "sip:UserB-dep@vm.wcom.com" maps to UserB's mailbox and the behavior
 of "generic message deposit"

Campbell & Sparks Informational [Page 24] RFC 3087 SIP Service Control April 2001

          User A              Proxy                VM Service
            |                   |                       |
            |  INVITE F1        |                       |
            |------------------>|                       |
            |                   |  INVITE F2            |
            | (100 Trying) F3   |---------------------->|
            |<------------------|                       |
            |                   |  200 OK F4            |
            |  200 OK F5        |<----------------------|
            |<------------------|                       |
            |                   |                       |
            |  ACK F6           |                       |
            |------------------>|  ACK F7               |
            |                   |---------------------->|
            |                   |                       |
            |      RTP Both Ways - Deposit Msg for B    |
            |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
            |                   |                       |
            |  BYE F8           |                       |
            |------------------>|  BYE F9               |
            |                   |---------------------->|
            |                   |                       |
            |                   |  200 OK F10           |
            |                   |<----------------------|
            |  200 OK F11       |                       |
            |<------------------|                       |
            |                   |                       |
   Flow Id                            Comments
  INVITE F1     INVITE sip:UserB-VM@vm.wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-VM@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Proxy-Authorization:Digest username="UserA",
                realm="MCI WorldCom SIP",
                nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                uri="sip:UserB-VM@wcom.com", response=<appropriately
                calculated hash goes here>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP

Campbell & Sparks Informational [Page 25] RFC 3087 SIP Service Control April 2001

                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
                /*Client for A prepares to receive data on port 49170
                from the network. */
  INVITE F2     INVITE sip:UserB-dep@vm.wcom.com SIP/2.0
  Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB-VM@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-VM@vm.wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  (100 Trying   SIP/2.0 100 Trying
  F3            Via: SIP/2.0/UDP here.com:5060
  Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-VM@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  200 OK F4     SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB-VM@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheLittleGuyVoiceMail <sip:UserB-
                dep@vm.wcom.com>
                Content-Type: application/sdp

Campbell & Sparks Informational [Page 26] RFC 3087 SIP Service Control April 2001

                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F5     SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:UserB-VM@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact TheLittleGuyVoiceMail <sip:UserB-
                dep@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  ACK F6        ACK sip:UserB-VM@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip:UserB-dep@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
  ACK F7        ACK sip:UserB-dep@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK

Campbell & Sparks Informational [Page 27] RFC 3087 SIP Service Control April 2001

                Content-Length: 0
                /* RTP streams are established between A and VM.  VM
                system starts IVR dialog for generic message-deposit
                for UserB */
                /* User A Hangs Up with VM system.  Alternatively, the
                VM system could initiate the BYE*/
  BYE F8        BYE sip:UserB-VM@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip:UserB-dep@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  BYE F9        BYE sip: UserB-dep@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F10    SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F11    SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: TheLittleGuyVoiceMail <sip:UserB-
                VM@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq:  2 BYE
                Content-Length: 0

Campbell & Sparks Informational [Page 28] RFC 3087 SIP Service Control April 2001

4.3 Message Retrieval Scenarios

4.3.1 Call to retrieve messages believed to be from a known subscriber

 Some user uses a SIP client on UserA's desk to call the voice mail
 system to retrieve messages.  The SIP client has authenticated itself
 to the proxy using credentials assigned to the device.  The proxy can
 make a weak assumption that the caller is the device owner.  The URI
 of "sip:UserA-retrieve@vm.wcom.com" maps to UserA's mailbox and the
 behavior of "retrieve messages after prompting for and verifying
 PIN." The VM System trusts the proxy, and will not accept calls from
 an untrusted source.  The proxy will not allow direct calls to
 UserA-retrieve@vm.wcom.com.  The proxy will forward calls placed to
 VoiceMail@wcom.com to UserA-retrieve@vm.wcom.com only for calls
 placed from a client device assigned to UserA.
          User A              Proxy                VM Service
            |                   |                       |
            |  INVITE F1        |                       |
            |------------------>|                       |
            |                   |  INVITE F2            |
            | (100 Trying) F3   |---------------------->|
            |<------------------|                       |
            |                   |  200 OK F4            |
            |  200 OK F5        |<----------------------|
            |<------------------|                       |
            |                   |                       |
            |  ACK F6           |                       |
            |------------------>|  ACK F7               |
            |                   |---------------------->|
            |                   |                       |
            |      RTP Both Ways - VM prompts for PIN
            |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
            |                   |                       |
            |  BYE F8           |                       |
            |------------------>|  BYE F9               |
            |                   |---------------------->|
            |                   |                       |
            |                   |  200 OK F10           |
            |                   |<----------------------|
            |  200 OK F11       |                       |
            |<------------------|                       |
            |                   |                       |

Campbell & Sparks Informational [Page 29] RFC 3087 SIP Service Control April 2001

   Flow Id                            Comments
  INVITE F1     INVITE sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Proxy-Authorization:Digest username="UserAPhone",
                realm="MCI WorldCom SIP",
                nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                uri="sip:VoiceMail@wcom.com", response=<appropriately
                calculated hash goes here>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
                /*Client for A prepares to receive data on port 49170
                from the network. */
  INVITE F2     INVITE sip:UserA-retrieve@vm.wcom.com SIP/2.0
  Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000

Campbell & Sparks Informational [Page 30] RFC 3087 SIP Service Control April 2001

  (100 Trying   SIP/2.0 100 Trying
  F3            Via: SIP/2.0/UDP here.com:5060
  Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  200 OK F4     SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: VoiceMailSystem <sip:UserA-
                retrieve@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F5     SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact VoiceMailSystem <sip: UserA-
                retrieve@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000

Campbell & Sparks Informational [Page 31] RFC 3087 SIP Service Control April 2001

  ACK F6        ACK sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip:UserA-retrieve@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
  ACK F7        ACK sip:UserA-retrieve@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>; tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
                /* RTP streams are established between A and VM.  VM
                determines that the call is likely from UserA, and
                starts a message retrieval session, prompting for
                PIN*/
                /* User A Hangs Up with VM system.  Alternatively, the
                VM system could initiate the BYE*/
  BYE F8        BYE sip: VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip:UserA-retrieve@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  BYE F9        BYE sip: UserA-retrieve@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F10    SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>

Campbell & Sparks Informational [Page 32] RFC 3087 SIP Service Control April 2001

                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F11    SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq:  2 BYE
                Content-Length: 0

4.3.2 Call to retrieve messages from an authenticated subscriber

 UserA to call the voice mail system to retrieve messages.
 Assumptions: The caller is authenticated using UserA's credentials.
 "sip:UserA-retrieve-auth@vm.wcom.com" maps to UserA's mailbox and the
 behavior of "retrieve messages." The voice mail service trusts the
 proxy not to forward any calls to that URI unless the call is
 authenticated to be from UserA.
 Given these assumptions, The VM service may choose not require a PIN
 for calls to this URI.

Campbell & Sparks Informational [Page 33] RFC 3087 SIP Service Control April 2001

          User A              Proxy                VM Service
            |                   |                       |
            |  INVITE F1        |                       |
            |------------------>|                       |
            |                   |  INVITE F2            |
            | (100 Trying) F3   |---------------------->|
            |<------------------|                       |
            |                   |  200 OK F4            |
            |  200 OK F5        |<----------------------|
            |<------------------|                       |
            |                   |                       |
            |  ACK F6           |                       |
            |------------------>|  ACK F7               |
            |                   |---------------------->|
            |                   |                       |
            |      RTP Both Ways - Deposit Msg for B    |
            |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
            |                   |                       |
            |  BYE F8           |                       |
            |------------------>|  BYE F9               |
            |                   |---------------------->|
            |                   |                       |
            |                   |  200 OK F10           |
            |                   |<----------------------|
            |  200 OK F11       |                       |
            |<------------------|                       |
            |                   |                       |
   Flow Id                            Comments
  INVITE F1     INVITE sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Proxy-Authorization:Digest username="UserA",
                realm="MCI WorldCom SIP",
                nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                uri="sip:VoiceMail@wcom.com", response=<appropriately
                calculated hash goes here>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP

Campbell & Sparks Informational [Page 34] RFC 3087 SIP Service Control April 2001

                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
                /*Client for A prepares to receive data on port 49170
                from the network. */
  INVITE F2     INVITE sip:UserA-retrieve-auth@vm.wcom.com SIP/2.0
  Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: TheBigGuy <sip:UserA@here.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserA 2890844526 2890844526 IN IP4 client.here.com
                s=Session SDP
                c=IN IP4 100.101.102.103
                t=0 0
                m=audio 49170 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  (100 Trying   SIP/2.0 100 Trying
  F3            Via: SIP/2.0/UDP here.com:5060
  Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Content-Length: 0
  200 OK F4     SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact: VoiceMailSystem <sip:UserA-retrieve-
                auth@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>

Campbell & Sparks Informational [Page 35] RFC 3087 SIP Service Control April 2001

                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  200 OK F5     SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                Record-Route: <sip:VoiceMail@wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 INVITE
                Contact VoiceMailSystem <sip: UserA-retrieve-
                auth@vm.wcom.com>
                Content-Type: application/sdp
                Content-Length: <appropriate value>
                v=0
                o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                s=Session SDP
                c=IN IP4 110.111.112.114
                t=0 0
                m=audio 3456 RTP/AVP 0
                a=rtpmap:0 PCMU/8000
  ACK F6        ACK sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route: <sip:UserA-retrieve-auth@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0
  ACK F7        ACK sip:UserA-retrieve-auth@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>; tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 1 ACK
                Content-Length: 0

Campbell & Sparks Informational [Page 36] RFC 3087 SIP Service Control April 2001

                /* RTP streams are established between A and VM.  VM
                determines that the call is likely from UserA, and
                starts a message retrieval session.  Since the proxy
                has already authenticated the identity of UserA, the
                VM does not need to prompt for PIN. */
                /* User A Hangs Up with VM system.  Alternatively, the
                VM system could initiate the BYE*/
  BYE F8        BYE sip:VoiceMail@wcom.com SIP/2.0
  A->Proxy      Via: SIP/2.0/UDP here.com:5060
                Route:<sip:UserA-retrieve-auth@vm.wcom.com>
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  BYE F9        BYE sip: UserA-retrieve-auth@vm.wcom.com SIP/2.0
  Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F10    SIP/2.0 200 OK
  VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq: 2 BYE
                Content-Length: 0
  200 OK F11    SIP/2.0 200 OK
  Proxy->A      Via: SIP/2.0/UDP here.com:5060
                From: TheBigGuy <sip:UserA@here.com>
                To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                Call-Id: 12345600@here.com
                CSeq:  2 BYE
                Content-Length: 0

Campbell & Sparks Informational [Page 37] RFC 3087 SIP Service Control April 2001

5. Security Considerations

 This document discusses a usage of SIP/2.0 as defined by RFC 2543[1].
 It introduces no additions, modifications, or restrictions to the
 protocol defined therein.  Any implementation of the concepts in this
 document is subject to the issues discussed there.

6. Acknowledgments

 The authors would like to thank Chris Cunningham, Steve Donovan, Alan
 Johnston, Henry Sinnreich, Kevin Summers, John Truetken, and Dean
 Willis for their discussion of and contribution to this work.

References

 [1] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg,
     "SIP: Session Initiation Protocol", RFC 2543, March 1999.

Authors' Addresses

 Ben Campbell
 dynamicsoft
 5100 Tennyson Parkway
 Suite 1200
 Plano, TX  75024
 EMail: bcampbell@dynamicsoft.com
 Robert J. Sparks
 dynamicsoft
 5100 Tennyson Parkway
 Suite 1200
 Plano, TX  75024
 EMail: rsparks@dynamicsoft.com

Campbell & Sparks Informational [Page 38] RFC 3087 SIP Service Control April 2001

Full Copyright Statement

 Copyright (C) The Internet Society (2001).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
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Campbell & Sparks Informational [Page 39]

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